1. Field of the Invention
The present invention related to a portable, internal combustion-engined tool, in particular, to a setting tool for driving in fastening elements, and including a drive piston having a piston rod for driving a fastening element, a combustion chamber located adjacent to the piston and in which a fuel gas mixture is ignited for generating pressure for driving the piston, at least one outlet valve provided in the combustion chamber for removing flue gases; a locking/unlocking device for closing and opening the at least one outlet valve, respectively; sensing means for retaining the locking/unlocking device in a locking position and having a member that is pressed against a circumference of the piston rod for retaining the locking/unlocking device in its locking position and that is displaced, after the piston reaches its initial position, into a path of the piston rod to enable displacement of the locking/unlocking device from the locking position into an unlocking position.
2. Description of the Prior Art
In the setting tools of the type described above, the drive energy is obtained by combustion of a fuel gas mixture, which drive energy is transmitted by the drive piston to a setting element. An ignitable fuel gas mixture is fed into the combustion chamber when the setting tool is pressed against an object into which a fastening element is to be driven in. Upon actuation of a trigger, an electrical spark is generated. The electrical spark ignites the fuel gas mixture, starting a combustion process that generates energy for driving the drive piston which adjoins the combustion chamber. At the end of its displacement in a setting direction, the drive piston passes past a plurality of outlet openings through which fuel gases can partially exit. After completion of a setting process, piston returns to its initial position as a result of underpressure created in the combustion chamber by cooling of the residual gases therein. During the time the piston returns to its initial position, the combustion chamber should remain sealed from the surrounding environment. The inlet/outlet valve, through which a fresh air is admitted into the combustion chamber, should only open after the completion of the return stroke of the drive piston. The time, which is necessary for returning of the drive piston to its initial position increases, with increase of the temperatures in the setting tool. In addition, high-energy tools require a large expansion volume which again leads to increase of the time necessary for returning the piston to its initial position.
It has been proposed to control the opening of the inlet/outlet valve dependent on the position of the piston, so that the valve would open only in a predetermined position of the piston or when the piston reaches its initial position. This permitted to prevent a premature opening of the inlet/outlet valve(s) and a resulting faulty positioning of the piston due to heating or other unfavorable conditions influencing the thermal feedback that provides for the return of the piston to its initial position. With this valve control, the position of the piston is determined, e.g., with a mechanical probe which is pressed against the piston.
Nevertheless, there is still a danger that the drive piston would not reach its initial position because of an increased friction which can be caused, e.g., by accumulation of dirt. Furthermore, there can exist operational conditions which would not provide for a reliable return of the drive piston into its initial position by a thermal feedback, e.g., at an increased heating of the tool.
In case the piston occupies a faulty position, the user has to have a possibility to bring the tool into its setting or initial position. This can be done by a manual displacement of the piston which, of course, is a serious drawback as it requires time and efforts. Alternatively, the setting tool can be equipped with a special device to that end. Such a device, e.g., is described in a German Publication DE-100 32 310.
DE-100 32 310 discloses a portable, internal combustion-engined setting tool for driving in fastening elements and including a drive piston, a combustion chamber having at least one outlet valve and in which a fuel gas mixture is ignited for generating pressure for driving the piston, and a locking/unlocking device for closing and opening the at least one outlet valve, respectively; sensing means for retaining the locking/unlocking device in a locking position and having a member that is pressed against a circumference of the piston rod for retaining the locking/unlocking device in the locking position and that is displaced, after the piston reaches its initial position, into a path of the piston rod to enable displacement of the locking/unlocking device from the locking position into an unlocking position.
In this type of setting tool, one or more mechanical elements, which provide for operation of the locking/unlocking device, are arranged in a plane in which the central axis of the piston rod is located, with a mechanical probe forming a pressure contact with the piston rod. Dependent on the position of the piston, these mechanical elements occupy different positions. If the piston has not returned to its initial position, these mechanical elements are deflected, keeping the inlet/outlet valve closed by retaining the locking/unlocking device in its locking position.
If the existing faulty position of the piston, which resulted, e.g., because of an increased friction caused by a dirt contamination, should be eliminated, with the conventional locking/unlocking device being used, the device is forcefully displaced into its unlocking position, whereby the inlet/outlet valve is open. This unlocking position is retained despite the probe being pressed against the piston rod and applying a force to the locking/unlocking device acting in the locking direction of the device. The drawback of this consists in that upon occurrence of the next setting process, when the setting tool is pressed against the object, the inlet/outlet valve self-locks again as a result of the probe being pressed against the piston rod. This means that the setting tool remains in its setting condition after it is lifted off the object. Thereby, a possibility of idle setting stroke exists that presents a security risk.
Accordingly, an object of the present invention is to provide a setting tool of the type discussed above and having a high safety standard and, in particular, with which a possibility of an idle setting stroke is eliminated.
This and other objects of the present invention, which will become apparent hereinafter, are achieved, by providing, in a setting tool of the type described above, means for positioning the member relative to the piston rod, when the piston is not in its initial position, so that the member does not apply to the locking/unlocking device a force acting in a locking direction of the locking/unlocking device.
The inventive setting tool has, in comparison with conventional tools, an additional degree of freedom which permits to manually displace the member, which contacts the piston rod, out of a plane of its normal movement, normal direction of movement, to provide for displacement of the locking/unlocking device into its unlocking position. Thereby, upon being displaced into the unlocking position, the locking/unlocking device is not subjected to any force that would bias the device to its locking position. As a result, upon the setting tool being pressed against an object, no self-locking of the inlet/outlet valve takes place as no locking force is applied by the sensing means. Thus, upon lifting of the setting tool of the object, the tool is not in the setting condition anymore, and an idle setting stroke cannot take place.
According to the present invention, at an incomplete return stroke of the piston, the sensing device does not apply to the locking/unlocking device a pressure force acting in the locking direction of the locking/unlocking device. The release position of the sensing means results from the sidewise position of the probe stylus when viewed in the sensing or press-on radial direction of the prove stylus. The same object is achieved when the sensing device (the probe holder) is pivoted in the other, opposite direction from its normal position. In the sidewise position of the probe stylus relative to the piston rod, the probe stylus does not transmit any pressure to the locking/unlocking device, and the locking/unlocking device is not biased into its locking direction.
According to a further advantageous embodiment of the present invention, there is provided preload means for biasing the probe stylus into engagement with the piston rod from the sidewise position of the probe stylus. The preload means does not have any force component that would bias the locking/unlocking device to its locking position. After the piston rod returns completely to its initial position, the probe stylus can again be returned into the path of the piston rod by the preload means for performing its usual task, namely, sensing the position of the piston rod. The preload means can comprise a suitable spring element.
According to another advantageous embodiment of the present invention, the locking/unlocking device can comprise a locking lever, with the sensing device being pivotally supported on the locking lever. With the locking lever extending parallel to the longitudinal axis of the piston rod in a spaced relationship to the piston rod and pivotable in the plane of the piston rod axis, the sensing device can be pivotally supported at the free end of the lever on a pivot axle secured to the lever. The pivot axle can lie in the pivot plane of the lever and be arranged so that the axle would extend transverse or substantially transverse to the piston rod axis. In this way, the sensing device can be pivoted out of the plane of the locking lever so that the sensing device or the probe stylus is located sidewise of the piston rod, without being supported by the piston rod. In this position, the sensing device does not transmits any force to the locking/unlocking device.
For pivoting the sensing device from its normal operational position, an actuation element is provided which can be manually operated. The actuation element pivots the sensing device against the biasing force of the preload means discussed above.
The novel features of the present invention, which are considered as characteristic for the invention, are set forth in the appended claims. The invention itself, however, both as to is construction and its mode of operation, together with additional advantages and objects thereof, will be best understood from the following detailed description of preferred embodiment, when read with reference to the accompanying drawings.